UCC28C43-Q1: External error amplifier connected to Pin "Comp" of UCC28C43QDRQ1

Giovanni Principato

Part Number: UCC28C43-Q1

Hello,

I made a Flyback converter with the UCC28C43-Q1 but I use an external error amplifier.

Can I put to GND "FB" Pin and overwrite the output with the external "Comp" signal?

Thanks in advance!

Best regards,

Giovanni

0 Hong Huang over 3 years ago

Hi,

No, if you tie IC FB to GND then the internal COMP will be always high and your external circuit cannot change COMP.

You should tie FB pin and COMP pin together so the internal COMP can follow your external signal on FB pin.

0 Giovanni Principato over 3 years ago in reply to Hong Huang

I tried to tie FB and Comp together but the COMP signal goes to the internal reference voltage of 2.5 V.

The internal comparator acts as a voltage follower not for my error signal but for the internal voltage reference.

How can I fix it?

0 Hong Huang over 3 years ago in reply to Giovanni Principato

Can you show your circuit how your external feedback connect to FB and COMP? It looks you have a gain match issue.

0 Giovanni Principato over 3 years ago in reply to Hong Huang

0 Hong Huang over 3 years ago in reply to Hong Huang

Hi,

Your circuit looks should work. Have you tried your circuit?

0 Giovanni Principato over 3 years ago in reply to Hong Huang

Hi,

yes, I have! but there are overcurrent problems with high load in turn on phase. Maybe because soft start don't work well with my configuration!

0 Hong Huang over 3 years ago in reply to Giovanni Principato

One way to add soft start can be found from this below application note, with Q3, R2 and C2.

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